Summary: Assay development for antibody against botulinum toxin will contribute to effective testing of regulated products by developing in vitro tests of toxin presence and potency. Current assays for botulinum toxin are based on mouse lethality and are therefore lengthy, expensive and imprecise. Most neutralizing antibody induced by botulinum toxoid vaccine is against the receptor binding domain. We propose to develop a convenient and sensitive method to measure this type of antibody. Assays for receptor binding will be developed by investigating the requirements for binding of botulinum toxins to gangliosides receptors. These studies will be done using chemically modified oligosaccharides derived from gangliosides and Biacore surface plasmon resonance. The information for learned form these studies will be used to develop ELISA-based assays that measure inhibition of binding by neutralizing antibodies to botulinum toxin.